Avian leukosis viruses (ALVs) and in vitro constructed recombinants of ALVs will be used to study the roles of viral and host genes in the induction of cancer. The molecular virology of four different virally induced cancers will be studied: B-cell lymphoma, erythroblastosis, angiosarcoma, and fibrosarcoma. The first specific aim is to define ALV sequences that determine lymphomogenic potential. These studies will focus on the roles of sequences near the 5' long terminal repeat (LTR) and at the 5' end of the env gene in cancer induction. These studies will also examine the role of deletions near the 5' LTR in the upregulation of c-myc transcription by ALV insertions. The second specific aim is to define the role of the C-terminal domain of the epidermal growth factor (EGF) receptor in the normal and malignant growth of erythroid, endothelial, and fibroblastic cells. These studies will define mutations in the C-terminal domain of the EGF receptor that determine the potential for viral-erbB genes to cause specific diseases. Studies will also be the C- terminal domain of the EGF receptor. The third specific aim is to define whether one or more than one gene determines the unusual susceptibility of inbred line 151 chickens to erythroblastosis induction by viral-erbB proteins encoding the complete C- terminus of the EGF receptor.